Air separator

ABSTRACT

An air separator oxygen gas capable of producing oxygen gas in an energy-saving manner, thereby remarkable downsizing can be realized. The air separator includes an air compressor ( 1 ) for taking in air from the outside and compressing it, first adsorption towers ( 2,3 ) for concentrating oxygen gas that is contained in the air compressed by the air compressor ( 1 ), an oxygen/air compressor ( 11 ) for further compressing oxygen-rich compressed air (X) passed through the first adsorption towers ( 2,3 ), a main heat exchanger ( 21 ) for cooling oxygen-rich compressed air (Y) passed through the oxygen/air compressor ( 11 ), and a high-pressure rectification tower ( 23 ) and a low-pressure rectification tower ( 28 ) for taking out oxygen gas by separating the oxygen-rich compressed air (Y) passed through the main heat exchanger ( 21 ) so as to be cooled to a low temperature by utilizing differences in boiling points of elemental gases.

TECHNICAL FIELD

The present invention relates to an air separator capable of producingoxygen gas in an energy-saving manner, thereby remarkable downsizing canbe realized.

BACKGROUND ARTS

Generally, a nitrogen gas (GN₂), an oxygen gas (GO₂), argon (Ar) and thelike are manufactured by the following steps. As shown in FIG. 6, air isused as a raw material and is compressed by an air compressor 61 and thethus compressed air is put into adsorption towers 62 for eliminatingwater (H₂O), carbon dioxide gas (CO₂) and hydrocarbon gas (C_(n)M_(m))from the compressed air by means of adsorption. Further, the thusobtained gas is passed through a main heat exchanger (not shown) in acold box 63 so as to be cooled to a super low temperature byheat-exchanging with refrigerant. Then, product gas (such as nitrogengas or oxygen gas) is manufactured by cryogenically separating the thuscooled gas in a rectification tower (not shown) and is passed throughthe main heat exchanger, so that the temperature of the product gas isincreased nearly to ambient temperature. An exhaust gas withdrawn fromthe cold box 63 is used for regenerating the adsorption towers 62 (see,for example, Japanese Unexamined Patent Publication No. 8-261644). InFIG. 6, a reference numeral 64 indicates a heater for regeneration andevacuation.

In such an air separator, an air compressor 61 having a dischargepressure of about 5 kg/cm²G (0.5 MPaG (gauge pressure)) is generallyused. The amount of air required for manufacturing oxygen gas of 10,000m³/h (Normal) by using such an air compressor 61 is calculated asfollows. Each rate (% by volume) of elements of air, that is, oxygen,nitrogen and argon, is 20.9%, 78.1% and 0.9%, respectively. Whenrecovery efficiency of oxygen gas is 97%, the amount of air istheoretically calculated by the formula of (10,000÷0.209)÷0.97. As aresult, about 50,000 m³/h (Normal) is determined as the air required.Therefore, the size of each of the adsorption towers 62, the main heatexchanger, the rectification tower and the like should be enlargedcorrespondingly for such an amount of air, which makes the apparatuslarge-sized as a whole. Further, when oxygen gas of 10,000 m³/h (Normal)is produced, the power required for working the air compressor 61 isabout 4500 kW (power required for compression is generally considered tobe equal to a value found by multiplying the required amount of air byabout 0.09), and the power required for working the heater 64 forregeneration and evacuation of the adsorption towers 62 is about 500 kW.In total, a great amount of power of about 5000 kW is required, whichmeans a significant energy required for manufacturing oxygen.

The present invention is made in view of such circumstances and it is anobject of the invention to provide an air separator capable ofmanufacturing oxygen gas in an energy-saving manner and that enablescryogenic separation mechanism and the like (a cold box and interiordevices therein) to be remarkably downsized.

DISCLOSURE OF THE INVENTION

In accordance with the present invention to achieve the aforesaidobject, there is provided an air separator including an air compressionmeans for taking in air from the outside and compressing it at a lowpressure, an oxygen concentrating means for concentrating oxygen gasthat is contained in the air compressed by the air compression means, anoxygen/air compression means for further compressing oxygen-richcompressed air (X), which has passed through the oxygen concentratingmeans, a heat exchanger for cooling oxygen-rich compressed air (Y),which has passed through the oxygen/air compression means, and arectification tower for taking out oxygen gas by separating theoxygen-rich compressed air (Y), which has passed through the heatexchanger so as to be cooled to a low temperature, by utilizingdifferences in boiling points of elemental gases.

According to the air separator of the present invention, raw-materialair is compressed at a low pressure by an air compression means, theconcentration of oxygen in the raw-material air is increased by anoxygen concentrating means, following the air compression means, forconcentrating oxygen gas in the thus compressed air, the thus obtainedgas is passed through an oxygen/air compression means and a heatexchanger, and then is supplied to a rectification tower. For thisreason, in the case where the same amount of oxygen gas or the like isproduced, energy can be greatly saved and also the amount of gas to becirculated through each means following the oxygen concentrating meanscan be reduced, so that each means can be downsized to a half size orless, which enables remarkable downsizing of the entire apparatus. Inthe present invention, “low pressure” in the above-mentioned contextmeans a pressure lower than the compression pressure caused by theoxygen/air compression means, and means generally not more thanone-third, preferably not more than one-fifth, and more preferably notmore than one-tenth of the compression pressure by the oxygen/aircompression means.

Where the oxygen concentrating means is an adsorption toweraccommodating an adsorbent for adsorbing nitrogen gas in the compressedair and impurities such as moisture in the compressed air are adsorbedby the adsorbent, the oxygen gas in the compressed air can beconcentrated by the action of the adsorbent of the adsorption tower andalso moisture in the compressed air can be eliminated so that theresultant gas to be compressed by the oxygen/air compression meansfollowing the oxygen concentrating means becomes drier and thus powerfor compression can further be reduced.

Where an elimination means for eliminating impurities in the oxygen-richcompressed air (Y) is provided between the oxygen/air compression meansand the heat exchanger, hydrocarbon, moisture, NO_(x) and the likeslightly remaining in the oxygen-rich compressed air (Y) can beeliminated, so that poor-quality air such as air in coastal areas(containing many sodium ions) and air alongside a street (containingmuch automotive exhaust gas) can be used as a raw-material air.

Where a part of the air compressed by the air compression means is notpassed through the oxygen concentrating means, but is supplied directlyto an inlet path for introducing the oxygen-rich compressed air (X)passed through the oxygen concentrating means into the oxygen/aircompression means, the part of the compressed air directly supplied tothe inlet path (after having passed through the air compression means)is allowed to merge into the remaining part of the compressed airsupplied to the inlet path (after having passed through the aircompression means and introduced into the oxygen concentrating means soas to become the oxygen-rich compressed air (X)), thereby theconcentration of oxygen in the oxygen-rich compressed air (X) can belowered. Therefore, when the amount of oxygen to be manufactured needsto be reduced, it can be realized by adjusting the amount of thecompressed air directly supplied to the inlet path.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a block diagram of one embodiment of an air separatoraccording to the present invention;

FIG. 2 is a block diagram of another embodiment of an air separatoraccording to the present invention;

FIG. 3 is a block diagram of a further embodiment of an air separatoraccording to the present invention;

FIG. 4 is a block diagram of a still further embodiment of an airseparator according to the present invention;

FIG. 5 is a block diagram of a still further embodiment of an airseparator according to the present invention; and

FIG. 6 is a block diagram of a conventional example.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram of one embodiment of an air separatoraccording to the present invention. In FIG. 1, a reference numeral 1indicates an air compressor (air compression means) for taking in airand compressing it, wherein a discharge pressure is low and about 0.1kg/cm²G (0.01 MPaG (gauge pressure)). A reference numeral 1 a indicatesa first feeding pipe for feeding compressed air passed through the aircompressor 1 into first adsorption towers 2, 3. The first adsorptiontowers (oxygen concentration means) 2, 3, are filled with an adsorbentsuch as silica gel at an upstream side thereof, and they are also filledwith a molecular sieve adsorbent developed by the present applicant(AW0203 available from Air Water Inc.) at a downstream side. The firstadsorption towers 2, 3 are aligned in pairs and one of them works foradsorption while the other works for regeneration, alternately. In thisembodiment, by means of the action of the adsorbent of the firstadsorption towers 2, 3 (nitrogen adsorption process), the amount (% byvolume) of each of the components of the low-pressure compressed airpassed through the air compressor 1 is arranged, for example, in such amanner that oxygen gas is about 50%, nitrogen gas is about 47.5% andargon gas is about 2.5%, respectively. The concentration of the oxygengas in the compressed air is increased from 20.9% by volume to 50% byvolume. The adsorption towers 2, 3 also eliminates water (H₂O), carbondioxide gas (CO₂), hydrocarbon gas (C_(n)M_(m)) and the like from thecompressed air by the action of the adsorbent, simultaneously with theabove-mentioned increase in oxygen concentration. A reference numeral 4indicates a vacuum pump for regeneration and evacuation of the firstadsorption towers 2, 3, and a reference numeral 4 a indicates a firstrelease pipe for releasing exhaust gas adsorbed by the adsorbent of thefirst adsorption towers 2, 3 into the atmosphere and regenerating theadsorbent. In this way, the system composed of the first adsorptiontowers 2, 3, and their pipes provided with open-close valves 6 a, 6 band 8 a, 8 b, respectively, and the vacuum pump 4 is a VSA (vacuum SwingAbsorbed) system, which is a membrane separation system, so that oneadsorption tower 2 (3) works for adsorption while the other tower 3 (2)is regenerated by means of vacuum suction by the vacuum pump 4. Further,a water separator (not shown) may be provided between the air compressor1 and the first adsorption towers 2, 3 for eliminating moisture from thecompressed air compressed by the air compressor, and, as required, aflon cooler (not shown) for cooling the compressed air passed throughthe water separator may be provided. In this embodiment, theabove-mentioned system is a VSA system, however, it may be a membraneseparation system such as a PSA (Pressure Swing Absorbed) system or aTSA (Thermal Swing Absorbed) system. In FIG. 1, reference numerals 6 a,6 b, 7 a, 7 b, 8 a and 8 b are open-close valves for conductingadsorption or regeneration of the first adsorption towers 2, 3,alternately.

A reference numeral 11 indicates a compact oxygen/air compressor(oxygen/air compression means) for further compressing the oxygen-richcompressed air (X) passed through the first adsorption towers 2, 3. (Asthe amount of gas to be circulated through the oxygen/air compressor canbe halved as compared with the conventional type, the oxygen/aircompressor can be downsized to a half size or less.) In this embodiment,a compact oxygen/air compressor (oilless centrifugal compressor having adischarge pressure of 5 kg/cm²G (0.5 MPaG (gauge pressure)) for furthercompressing the oxygen-rich compressed air (X) is used as the compactoxygen/air compressor 11. The oxygen/air compressor 11 is an oillessmechanism to prevent explosion in further compressing the oxygen-richcompressed air (X). A reference numeral 11 a indicates a second feedingpipe for feeding the oxygen-rich compressed air (Y) passed through theoxygen/air compressor 11 to second adsorption towers 12, 13. Theadsorption towers 12, 13, each filled with an adsorbent such as acommercially available molecular sieve, are aligned in pairs and one ofthem works for adsorption while the other works for regeneration,alternately (and is a compact size of half or less as compared with theconventional type) for eliminating water (H₂O), carbon dioxide gas,C_(n)M_(m), NO_(x) and the like slightly remaining in the oxygen-richcompressed air (Y) further compressed by the oxygen/air compressor 11. Areference numeral 14 indicates a second release pipe for releasingexhaust gas, which has finished the regeneration process in the secondadsorption towers 12, 13, into the atmosphere. The system composed ofthe second adsorption towers 12, 13, and their pipes provided withopen-close valves 16 a, 16 b and 19 a, 19 b, respectively, is a TSAsystem. In FIG. 1, reference numerals 16 a, 16 b, 17 a, 17 b, 18 a, 18b, 19 a and 19 b are open-close valves for conducting adsorption orregeneration of the second adsorption towers 12, 13, alternately.

A reference numeral 21 indicates a main heat exchanger such as aplate-fin exchanger, which cools the oxygen-rich compressed air (Y),wherein minute amounts of water, carbon dioxide gas and the likeremaining are eliminated by means of adsorption by adsorption towers 12,13, to a super low temperature. As the amount of gas to be circulatedthrough the main heat exchanger 21 to be processed therein can also behalved as compared with the conventional type, the main heat exchangercan be downsized to a half size or less. A reference numeral 22indicates a supply pipe for supplying the oxygen-rich compressed air (Y)cooled to a super low temperature by the main heat exchanger 21 into alower part of a high-pressure rectification tower 23. As the amount ofgas to be circulated through the high-pressure rectification tower (acolumn plate type or a packed column type) 23 can be halved as comparedwith that of the conventional type, the half or less capacity of thehigh-pressure rectification tower is enough and thus the size thereofcan be downsized to half or less. In the high-pressure rectificationtower 23, liquid oxygen-rich liquid air 24 of the oxygen-rich compressedair (Y) fed through the supply pipe 22 accumulates in the bottomportion, while nitrogen gas rises. A part of the rising nitrogen gas ispassed through a first reflux pipe 31 and introduced into a condenser 30positioned in a lower portion of a low-pressure rectification tower 28,while the remaining part thereof is passed through a nitrogen takeoutpipe 26 and activates an expansion turbine 37. The nitrogen gasintroduced into the condenser 30 is liquefied so as to become liquidnitrogen. The nitrogen gas thus liquefied is returned through a secondreflux pipe 32 to an upper portion of the high-pressure rectificationtower 23 as a reflux liquid, and flows downward in the high-pressurerectification tower 23, and then contacts in a countercurrent manner theoxygen-rich compressed air (Y) rising from the bottom, therebyliquefying a high-boiling point elemental gas (oxygen gas) in theoxygen-rich compressed air (Y), which flows downward. For this reason,the liquid oxygen-rich liquid air 24 is accumulated in the bottom so asto be further oxygen-rich, while a low-boiling elemental gas (nitrogengas) rises upward in the high-pressure rectification tower 23. Thenitrogen gas withdrawn through the nitrogen takeout pipe 26 is suppliedto the main heat exchanger 21 so as to cool compressed air passedthrough the main heat exchanger 21, and is supplied through a firstconnecting pipe 26a to an expansion turbine 37 so as to be a drivingsource for the expansion turbine 37, as mentioned above, to generatecold. A reference numeral 38 indicates a bypass provided with anopen-close valve 38 a. In other words, the nitrogen gas introducedthrough the nitrogen takeout pipe 26 and the first connecting pipe 26 aprovided with the open-close valve 26 b into the expansion turbine 37expands therein and conducts thermodynamic external work, so that thenitrogen gas is cooled to an extremely low temperature to generate coldin an amount required for the air separator. The nitrogen gas in such astate is supplied through a second connecting pipe 37 a into the mainheat exchanger 21 wherein the nitrogen gas itself becomes ambienttemperature by heat exchanging with a raw material air for imparting thecold to the raw material air. Most of such nitrogen gas is passedthrough a release pipe 37 b and is released into the atmosphere as anexhaust gas, while a part thereof is passed through a branch pipe 40 soas to regenerate an adsorbent of the second adsorption towers 12, 13.The branch pipe 40 functions for supplying the introduced nitrogen gasinto either a first pipe 42 provided with a heater 41 or a second pipe43 without a heater. A reference numeral 44 indicates a third pipe forsupplying nitrogen gas passed through the first pipe 42 or the secondpipe 43 into the second adsorption towers 12, 13 for regenerating theadsorbent.

A reference numeral 28 indicates a low-pressure rectification tower (acolumn plate type or a packed column type) located above thehigh-pressure rectification tower 23. The liquid oxygen-rich liquid air24 accumulated in the bottom of the high-pressure rectification tower 23is fed through a feeding pipe 29 provided with an expansion valve 29 ainto the low-pressure rectification tower 28. The low-pressurerectification tower 28 contains the condenser 30 in the bottom thereofinto which a part of nitrogen gas withdrawn from the high-pressurerectification tower 23 is introduced through the first reflux pipe 31.The thus withdrawn nitrogen gas heats liquid oxygen 34 (LO₂: purity ofabout 99.7% by volume) accumulated in the bottom of the low-pressurerectification tower 28 so as to be evaporated while the nitrogen itselfliquefies due to coldness of the liquid oxygen 34 and a part thereof isreturned through the second reflux pipe 32 provided with a flowadjusting valve 32 a to the upper part of the high-pressurerectification tower 23 as a reflux liquid, as mentioned above. Theremaining part of the liquid nitrogen 34 is introduced through a branchpipe 33 provided with a flow adjusting valve 33 a into the upper part ofthe low-pressure rectification tower 28 as a reflux liquid and flowsdown through the low-pressure rectification tower 28 for gas-liquidseparation. A reference numeral 35 indicates a product oxygen gastakeout pipe extended from the lower part of the low-pressurerectification tower 28. The product oxygen gas takeout pipe 35 takes outhigh-purity oxygen gas evaporated from the liquid oxygen 34 accumulatedin the bottom of the low-pressure rectification tower 28 and feeds thethus withdrawn oxygen gas to the main heat exchanger 21 forheat-exchange with the oxygen-rich compressed air (Y) so that the oxygengas itself becomes ambient temperature and then is released to theoutside of the apparatus as product oxygen. A reference numeral 36indicates a product nitrogen gas takeout pipe extended from the upperpart of the low-pressure rectification tower 28. The product nitrogengas takeout pipe 36 takes out nitrogen gas rising upwards in thelow-pressure rectification tower 28 and feeds the thus withdrawnnitrogen gas to the main heat exchanger 21 for cooling the oxygen-richcompressed air (Y), so that the nitrogen gas itself becomes ambienttemperature and then is released to the outside of the apparatus asproduct nitrogen gas. A reference numeral 39 is a cold box into whichheat insulating material such as perlite (not shown) is packed forlow-temperature insulation. In this embodiment, oxygen is concentratedby adsorbing nitrogen gas in the first adsorption towers 2, 3, however,an adsorbent for adsorbing oxygen gas may be used, so that oxygen gasmay be adsorbed, and the thus obtained oxygen gas is concentrated, andthen withdrawn.

The nitrogen gas and the oxygen gas are manufactured by using thisapparatus in the following manner. That is, air is taken into the aircompressor (air compression means) 1 from the outside so as to becompressed at a low pressure, and moisture in the compressed air iseliminated by the water separator (not shown), and then the air in sucha state is fed into the first adsorption towers (oxygen concentratingmeans) 2, 3, so that nitrogen gas, moisture, carbon dioxide gas,hydrocarbon gas (C_(n)M_(m)) and the like from the compressed air areeliminated by means of adsorption, thereby oxygen gas in the compressedair is concentrated, which is a main feature of the present invention.In turn, the oxygen-rich compressed air (X) from the first adsorptiontowers 2, 3 is introduced into the oxygen/air compressor (oxygen/aircompression means) 11 for further compressing the oxygen-rich compressedair (X) for obtaining the oxygen-rich compressed air (Y). Theoxygen-rich compressed air (Y) is fed into the second adsorption towers12, 13 for eliminating water, carbon dioxide gas, NO_(x) and the like inthe oxygen-rich compressed air (Y) Successively, the oxygen-richcompressed air (Y), from which water, carbon dioxide gas, No_(x) and thelike have been eliminated by adsorption, is fed into the main heatexchanger 21 so as to be cooled to a super low temperature, and isintroduced into the lower part of the high-pressure rectification tower23 in such a state. In the high-pressure rectification tower 23, theoxygen-rich compressed air (Y) is brought into contact with refluxliquid produced in the low-pressure rectification tower 28 in acountercurrent manner for purifying the compressed air, therebyliquefying a high-boiling point elemental gas (oxygen gas) in theoxygen-rich compressed air (Y), thereby leaving nitrogen in a gaseousstate by using the difference in boiling point between nitrogen andoxygen (boiling point for oxygen of −183° C., that for nitrogen of −196°C.). The nitrogen gas is withdrawn through the nitrogen takeout pipe 26,and is supplied to the main heat exchanger 21, and then is supplied tothe expansion turbine 37 so as to generate cold. Most of such nitrogengas is released to the outside of the apparatus while a part thereof isused for regenerating the second adsorption towers 12, 13.

Then nitrogen gas accumulated in the upper part of the low-pressurerectification tower 28 is taken out through the product nitrogen gastakeout pipe 36 is fed into the main heat exchanger 21 so as to beheated nearly to the ambient temperature, and then released to theoutside of the apparatus as product nitrogen gas. On the other hand, theliquid oxygen-rich liquid air 24 accumulated in the bottom of thehigh-pressure rectification tower 23 is fed through a feeding pipe 29into the low-pressure rectification tower 28, and liquid oxygen 34,wherein nitrogen has been evaporated and eliminated, is accumulated inthe bottom of the low-pressure rectification tower 28 and is heatexchanged with nitrogen gas passed through the condenser 30 positionedin the bottom of the low-pressure rectification tower 28 so as to beevaporated. The thus evaporated oxygen gas is withdrawn through theproduct gas takeout pipe 35, and is fed into the main heat exchanger 21so as to be heated nearly to the ambient temperature, and then isreleased to the outside of the apparatus as a product oxygen gas. Thus,product oxygen gas and product nitrogen gas can be obtained.

In this embodiment, the concentration of oxygen in the compressed air isincreased from 20.9% by volume to about 50% by volume by the firstadsorption towers 2, 3. The amount of air required for manufacturingoxygen gas of 10,000 m³/h (Normal) is calculated as follows. Whenrecovery efficiency of oxygen gas is 97%, the amount of air istheoretically calculated by the formula of (10,000÷0.500)÷0.97. As aresult, about 20,600 m³/h (Normal) is determined as the air required,which is reduced to about 41% as compared with that required in theconventional apparatus mentioned at the beginning of the presentspecification. Further, when oxygen gas of 10,000 m³/h (Normal) isproduced, the power required for working the oxygen/air compressor 11 isreduced to about 2000 kW, and it is thought that the power required forworking the oxygen/air compressor 1 is about 300 kW, the power requiredfor working the vacuum pump 4 is about 900 kW, and the electrical powerfor the electrical heater 41 is about 200 kW. The total amount is about3400 kW, reduced to about 70% as compared with the conventionalapparatus. Therefore, energy can be saved by 30% or more.

Further, in this embodiment, the first adsorption towers 2, 3 areprovided for increasing the concentration of the oxygen gas in thecompressed air obtained by compressing air as raw material by the aircompressor 1. The thus obtained gas is fed through the oxygen/aircompressor 11 and the main heat exchanger 21 into the high-pressurerectification tower 23 and the low-pressure rectification tower 28. Forthis reason, the amount of gas to be circulated through each device suchas the main heat exchanger 21 and both of the rectification towers 23,28 following the oxygen/air compressor 11, can be reduced, so that eachdevice can be downsized to a half size or less, which enables remarkabledownsizing of the entire apparatus.

For example, when oxygen gas of 70,000 m³/h (Normal) is produced, thehigh-pressure rectification tower 23 has a diameter of 7 m in theconventional apparatus (according to the calculated value by theapplicant). Since there is no means for transporting such ahigh-pressure rectification tower, there is no choice but to assemble iton site. However, when the same amount of oxygen gas is produced in thisembodiment, the amount of gas to be circulated through the rectificationtower can be halved, so that the diameter of the rectification tower canbe reduced to about 4.2 m. For this reason, it is possible to transportthe rectification tower assembled in a plant to a site, resulting ingreat laborsaving.

FIG. 2 illustrates another embodiment of an air separator according tothe present invention. In this embodiment, second adsorption towers 12,13 are eliminated. In other words, second adsorption towers 12, 13, asecond release pipe 14, pipes provided with open-close valves 16 a, 16b, 17 a, 17 b, 18 a, 18 b, 19 a and 19 b, a branch pipe 40, first tothird pipes 42 to 44 are eliminated. Except for that, this embodiment isthe same as the above-mentioned embodiment and similar parts are denotedby the same reference numerals. When the apparatus of this embodiment isinstalled in the place where clean air is used as a raw material, thesame effects as in the above-mentioned embodiment can be obtained andalso the apparatus can be simplified and downsized.

FIG. 3 illustrates a further embodiment of an air separator according tothe present invention. In this embodiment, a liquid oxygen tank (notshown) into which liquid oxygen (LO₂) is supplied from the outside ofthe apparatus by means of a tanker or the like is used instead of anexpansion turbine 37 in the embodiment as shown in FIG. 2. Except thatsuch liquid oxygen is used as a cold source, this embodiment issubstantially the same as that shown in FIG. 2. In FIG. 3, a referencenumeral 47 indicates an inlet pipe for introducing the liquid oxygenfrom the liquid oxygen tank into the lower part of a low-pressurerectification tower 28 as a cold source. The liquid oxygen introduced bythe inlet pipe 47 flows downward to the bottom of the low-pressurerectification tower 28 and joins liquid oxygen 34 accumulated in thebottom thereof. A reference numeral 48 indicates an exhaust pipeextended from the low-pressure rectification tower 28 for withdrawingnitrogen gas (exhaust GN₂) accumulated in the upper part of each shelf(or packed column) of the low-pressure rectification tower 28 so as tobe introduced into a supercooler 49. The exhaust pipe 48 leads theexhaust nitrogen gas passed through the supercooler 49 into a main heatexchanger 21 for cooling the oxygen-rich compressed air (Y) and releasesthe exhaust nitrogen gas to the outside. The supercooler 49, throughwhich are passed: a) oxygen-rich liquid air 24 via a feeding pipe 29; b)liquid nitrogen (reflux liquid) via a branch pipe 33; c) productnitrogen gas via a product nitrogen gas takeout pipe 36; and d) exhaustnitrogen gas via the exhaust pipe 48, works for cooling the oxygen-richliquid air 24 a). A reference numeral 50 indicates a liquid oxygentakeout pipe extended from the bottom of the low-pressure rectificationtower 28. The liquid oxygen takeout pipe 50 takes out liquid oxygenaccumulated in the bottom of the low-pressure rectification tower 28,which is led into the main heat exchanger 21 for cooling the oxygen-richcompressed air (Y), and also heating the liquid oxygen itself up toambient temperature for obtaining product oxygen gas, and introduces thethus obtained product oxygen gas into a product oxygen gas takeout pipe35. A reference numeral 51 indicates a product nitrogen gas compressorinstalled in a product nitrogen takeout pipe 36 for increasing thepressure of the product nitrogen gas passing through the productnitrogen gas takeout pipe 36 to a specified pressure. A referencenumeral 52 indicates a first product oxygen gas compressor installed inthe product oxygen gas takeout pipe 35 for increasing the pressure ofthe product oxygen gas passing through the product oxygen gas takeoutpipe 35 to a specified pressure and feeding the product oxygen gas intoa low pressure product oxygen gas takeout pipe 53. A reference numeral54 indicates a second product oxygen gas compressor for furtherincreasing the pressure of the product oxygen gas passed through thefirst product oxygen gas compressor 52 and feeding the product oxygengas into a high pressure product oxygen gas takeout pipe 55. In thisembodiment, the ceiling of the high-pressure rectification tower 23 andthe bottom of the low-pressure rectification tower 28 located above thehigh-pressure rectification tower 23 are formed integrally by the samematerial. In FIG. 3, a reference numeral 36 a indicates a pipe forfeeding a product nitrogen gas passing through the product nitrogentakeout pipe 36 into an exhaust pipe 48. A reference numeral 39A is acold box in which an insulating material such as perlite is filled andvacuum sucked. Except for that, this embodiment is the same as thatshown in FIG. 2 and similar parts are denoted by the same referencenumerals.

The nitrogen gas and the oxygen gas are manufactured by using thisapparatus in the following manner. That is, in the same manner as in theembodiment as shown in FIG. 2, air is taken into the air compressor (aircompression means) 1 from the outside in which air is compressed at alow pressure, and moisture in the compressed air is eliminated by thewater separator (not shown), and then the air in such a state is fedinto the first adsorption towers (oxygen concentrating means) 2, 3, sothat nitrogen gas, moisture, carbon dioxide gas, hydrocarbon gas(C_(n)M_(m)) and the like in the compressed air are eliminated by meansof adsorption, thereby the concentration of oxygen gas in the compressedair is increased. In turn, the oxygen-rich compressed air (X) from thefirst adsorption towers 2, 3 is introduced into the oxygen/aircompressor (oxygen/air compression means) 11 for further compressing theoxygen-rich compressed air (X) for obtaining the oxygen-rich compressedair (Y). The oxygen-rich compressed air (Y) is fed into the main heatexchanger 21 to be cooled to a super low temperature and is introducedinto a lower part of a high-pressure rectification tower 23 in such astate. In the high-pressure rectification tower 23, the oxygen-richcompressed air (Y) is brought into contact with reflux liquid producedin the low-pressure rectification tower 28 in a countercurrent mannerfor purifying the compressed air, thereby liquefying a high-boilingpoint elemental gas (oxygen gas) in the oxygen-rich compressed air (Y),thereby leaving nitrogen in a gaseous state by using the difference inboiling point between nitrogen and oxygen (boiling point for oxygen of−183° C., that for nitrogen of −196° C.)

Then, nitrogen gas accumulated in the upper part of the low-pressurerectification tower 28 is taken out through the product nitrogen gastakeout pipe 36, and is fed into the supercooler (heat exchanger) 49,and then is fed into the main heat exchanger 21 so as to be heatednearly to the ambient temperature, and finally is released to theoutside of the apparatus as product nitrogen gas. On the other hand, theoxygen-rich liquid air 24 accumulated in the bottom of the high-pressurerectification tower 23 is fed through a feeding pipe 29 into thesupercooler 49 so as to be cooled. The oxygen-rich liquid air 24 in agas-liquid mixing state is fed into the low-pressure rectification tower28, wherein nitrogen has been evaporated and eliminated, so that liquidoxygen 34 is accumulated in the bottom of the low-pressure rectificationtower 28 and is heat exchanged with nitrogen gas passed through thecondenser 30 positioned in the bottom of the low-pressure rectificationtower 28 so as to be evaporated. The thus evaporated oxygen gas iswithdrawn through the product oxygen gas takeout pipe 35, and is fedinto the main heat exchanger 21 so as to be heated nearly to the ambienttemperature, and then is released through a low-pressure product oxygengas takeout pipe 53 via a first product oxygen gas compressor 52 to theoutside of the apparatus as product oxygen gas and is also releasedthrough a high-pressure product oxygen takeout pipe 55 via a secondproduct oxygen gas compressor 54 to the outside of the apparatus asproduct oxygen gas. Thus, the product oxygen gas and the productnitrogen gas can be obtained.

As mentioned above, the same effects and advantages are obtained in thisembodiment as well as in the embodiment as shown in FIG. 2.

FIG. 4 illustrates a still further embodiment of an air separatoraccording to the present invention. In this embodiment, a liquidnitrogen tank (not shown) into which liquid nitrogen (LN_(z)) issupplied from the outside of the apparatus by means of a tanker or thelike is used instead of an expansion turbine 37 in the embodiment asshown in FIG. 2. Except that such liquid nitrogen is used as a coldsource, this embodiment is substantially the same as that shown in FIG.2. In FIG. 4, a reference numeral 47 a indicates an inlet pipe forintroducing the liquid nitrogen from the liquid nitrogen tank into theupper part of a high-pressure rectification tower 23 as a cold source.The liquid nitrogen introduced through the inlet pipe 47 a and a part ofthe liquid nitrogen liquefied in a condenser 30 positioned in a lowerpart of a low-pressure rectification tower 28 are introduced into anupper part of the high-pressure rectification tower 23. Except for that,this embodiment is the same as that shown in FIG. 2 and similar partsare denoted by the same reference numerals.

FIG. 5 illustrates a still further embodiment of an air separatoraccording to the present invention. In this embodiment, the firstfeeding pipe 1 a for feeding the compressed air which has passed throughthe air compressor 1 into first adsorption towers 2, 3 and an inlet pipe57 (a reference numeral 57 is not denoted in FIG. 1) for introducing theoxygen-rich compressed air (X), which has passed through the firstadsorption towers 2, 3, into the oxygen/air compressor 11 (as in theembodiment as shown in FIG. 1) are connected with a connecting pipe 58provided with an open-close valve (or a flow adjusting valve) 58 a. Apart of the compressed air which has passed through the air compressor 1and a water separator (not shown) is fed directly through the connectingpipe 58 into the inlet pipe 57 by opening the open-close valve 58 a(i.e., instead of being passed through the adsorption towers 2, 3), andthe remaining part is passed through the adsorption towers 2, 3 andintroduced into the inlet pipe 57, so that both are allowed to join inthe inlet pipe 57. Thus, the concentration of the oxygen gas of theremaining part of the compressed air introduced through the firstadsorption towers 2, 3 into the inlet pipe 57 is diluted with the partof the compressed air introduced through the connecting pipe 58 into theinlet pipe 57. Except for that, this embodiment is the same as thatshown in FIG. 1 and similar parts are denoted by the same referencenumerals. The same effects and advantages are obtained in thisembodiment as well as in the embodiment as shown in FIG. 1. Further,since the concentration of the oxygen gas in the compressed air suppliedinto the lower part of the high-pressure rectification tower 23 islowered, the amount of the product oxygen gas can be reduced. Therefore,when the amount of the product oxygen gas is needed to be reduced, thisembodiment enables to reduce it, correspondingly. Such a connecting pipe58 provided with an open-close valve 58 a can be used in the embodimentsas shown in FIG. 2 to FIG. 4.

1. An air separator comprising an air compression means for taking inair from the outside and compressing it at a low pressure, an oxygenconcentrating means for concentrating oxygen gas that is contained inthe air compressed by the air compression means, an oxygen/aircompression means for further compressing oxygen-rich compressed air (X)passed through the oxygen concentrating means, a heat exchanger forcooling oxygen-rich compressed air (Y) passed through the oxygen/aircompression means, and a rectification tower for taking out oxygen gasby separating the oxygen-rich compressed air (Y) passed through the heatexchanger so as to be cooled to a low temperature by utilizingdifferences in boiling points of elemental gases, wherein the aircompression means, the oxygen concentrating means and the oxygen/aircompression means are arranged in one line and the total amount of thecompressed air compressed by the air compression means is supplied tothe oxygen/air compression means.
 2. An air separator as set forth inclaim 1, wherein the oxygen concentrating means is an adsorption towercontaining an adsorbent for adsorbing nitrogen gas in the compressedair, the adsorbent capable of also adsorbing impurities such as moisturein the compressed air.
 3. An air separator as set forth in claim 1,further comprising an elimination means for eliminating impurities inthe oxygen-rich compressed air (Y) between the oxygen/air compressionmeans and the heat exchanger.
 4. An air separator as set forth in claim2, further comprising an elimination means for eliminating impurities inthe oxygen-rich compressed air (Y) between the oxygen/air compressionmeans and the heat exchanger.
 5. An air separator as set forth in claim1, wherein a part of the air compressed by the air compression means isnot passed through the oxygen concentrating means, but is directlysupplied to an inlet path for introducing the oxygen-rich compressed air(X) passed through the oxygen concentrating means into the oxygen/aircompression means.
 6. An air separator as set forth in claim 2, whereina part of the air compressed by the air compression means is not passedthrough the oxygen concentrating means, but is directly supplied to aninlet path for introducing the oxygen-rich compressed air (X) passedthrough the oxygen concentrating means into the oxygen/air compressionmeans.
 7. An air separator as set forth in claim 3, wherein a part ofthe air compressed by the air compression means is not passed throughthe oxygen concentrating means, but is directly supplied to an inletpath for introducing the oxygen-rich compressed air (X) passed throughthe oxygen concentrating means into the oxygen/air compression means. 8.An air separator as set forth in claim 4, wherein apart of the aircompressed by the air compression means is not passed through the oxygenconcentrating means, but is directly supplied to an inlet path forintroducing the oxygen-rich compressed air (X) passed through the oxygenconcentrating means into the oxygen/air compression means.